It is sometimes desired to promote stiffness for a rubber composition, particularly for a tire component such as for example a tire tread, sidewall apex and sidewall insert.
In practice, stiffness of various rubber components of a tire may desirable to promote handling of the tire such as, for example, steering and cornering.
Historically, stiffness of rubber compositions, particularly cured rubber composition containing diene-based elastomers, may be promoted, for example, by an inclusion of a dispersion of various short fibers and by inclusion of a resin product of methylene donor and methylene acceptor and by providing an increase in reinforcing filler content.
However, hysteresis of a rubber composition may also normally promoted as evidenced by an decrease in its rebound and an increase in its tan delta, physical properties which, in turn, promotes an increase in its internal heat generation, and an accompanying temperature rise, as the rubber composition is being worked as in a component of a tire during service and operation of the tire.
An indication of stiffness of a sulfur cured rubber composition may be evidenced by one or more of the rubber composition's physical properties such as, for example, storage modulus (G′), and tensile modulus (e.g. 300 percent modulus).
For this invention, it is desired to evaluate increasing stiffness of a rubber composition without significantly increasing its hysteresis, namely without making the rubber composition significantly more hysteretic.
It is desired to evaluate promoting stiffness of a cured rubber composition by inclusion of a dispersion of short fibers together with resin product of a methylene donor and a methylene acceptor where at least a portion of the methylene acceptor is comprised of epoxidized phenol formaldehyde polymer.
For this evaluation, the resin product may be provided as a reaction product of the methylene donor and methylene acceptor in situ within the rubber composition or as a product of a pre-formed initial resin thereof with a molar deficiency of the methylene donor followed by reaction therewith by the same or different methylene donor in situ within the rubber composition so long as with the methylene acceptor reacted in situ within the rubber composition is comprised of an epoxidized phenol formaldehyde polymer.
In the description of this invention, the term “phr” relates to parts by weight for a material or ingredient per 100 parts by weight elastomer(s)”. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.